Systems and methods for providing an envelope tracking supply voltage

ABSTRACT

Envelope tracking power supply circuitry includes a look up table (LUT) configured to provide a target supply voltage based on a power envelope measurement. The target supply voltage is dynamically adjusted based on a delay between the power envelope of an RF signal and a provided envelope tracking supply voltage. The envelope tracking supply voltage is generated from the adjusted target supply voltage in order to synchronize the envelope tracking supply voltage with the power envelope of the RF signal.

RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 63/064,773, filed Aug. 12, 2020, provisional patent applicationSer. No. 63/064,784, filed Aug. 12, 2020, provisional patent applicationSer. No. 63/090,566, filed Oct. 12, 2020, provisional patent applicationSer. No. 63/090,574, filed Oct. 12, 2020, provisional patent applicationSer. No. 63/090,583, filed Oct. 12, 2020, and provisional patentapplication Ser. No. 63/112,430, filed Nov. 11, 2020, the disclosures ofwhich are hereby incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure is related to systems and methods for providingan envelope tracking supply voltage, and in particular to systems andmethods for providing an envelope tracking supply voltage for radiofrequency (RF) signals.

BACKGROUND

Envelope tracking power supplies for radio frequency (RF) poweramplifiers enable increased linearity and efficiency by providing asupply voltage that tracks a power envelope of an RF signal. Due to themechanics associated with generating the signal, an envelope trackingsupply voltage may be delayed or advanced with respect to the RF signal.This may cause excessive power consumption, compression, and/or clippingin the RF power amplifier. Conventional synchronization between envelopetracking power supply signals and RF signals often fails to adequatelysynchronize the signals, especially for high bandwidth signals such asthose for fifth generation (5G) and mmWave applications. Accordingly,there is a need for improved systems and methods for providing anenvelope tracking supply voltage.

SUMMARY

In one embodiment, envelope synchronization circuitry includes a targetvoltage input node, an inverted target voltage input node, anoperational amplifier, a first adjustable resistor, a second adjustableresistor, a capacitor, a first switch, and a second switch. A targetvoltage is provided at the target voltage input node and an invertedtarget voltage is provided at the inverted target voltage input node.The operational amplifier includes an inverting input, a non-invertinginput, and an output. The non-inverting input is coupled to a fixedpotential. An adjusted target supply voltage is provided at the output.The first adjustable resistor is coupled between the target voltageinput and the inverting input of the operational amplifier. The secondadjustable resistor is coupled between the inverting input of theoperational amplifier and the output of the operational amplifier. Thecapacitor is coupled between the inverting input and an intermediatenode. The first switch is coupled between the intermediate node and thetarget voltage input. The second switch is coupled between the invertedtarget voltage input and the intermediate node. The topology of theenvelope synchronization circuitry allows for providing a delayed oradvanced version of the target voltage, depending on the orientation ofthe first switch and the second switch and the resistance chosen for thefirst resistor and the second resistor.

In another aspect, any of the foregoing aspects individually ortogether, and/or various separate aspects and features as describedherein, may be combined for additional advantage. Any of the variousfeatures and elements as disclosed herein may be combined with one ormore other disclosed features and elements unless indicated to thecontrary herein.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 is a functional schematic illustrating a radio frequency (RF)system according to one embodiment of the present disclosure.

FIG. 2 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 3 is a graph illustrating an RF signal, corresponding powerenvelope, and an envelope tracking supply voltage according to oneembodiment of the present disclosure.

FIG. 4A is a graph illustrating an isogain contour for an RF poweramplifier and corresponding slope adjustments according to oneembodiment of the present disclosure.

FIG. 4B is a graph illustrating an RF signal and corresponding envelopetracking supply voltages according to one embodiment of the presentdisclosure.

FIG. 5 is a graph illustrating an isogain contour for an RF poweramplifier and corresponding slope and maximum voltage adjustmentsaccording to one embodiment of the present disclosure.

FIG. 6 is a graph illustrating an RF signal and corresponding envelopetracking supply voltages according to one embodiment of the presentdisclosure.

FIG. 7 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 8 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 9 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 10 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 11 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 12 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 13 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 14 is a graph illustrating an RF signal and corresponding envelopetracking supply voltages according to one embodiment of the presentdisclosure.

FIG. 15 is a graph illustrating a number of envelope tracking supplyvoltages according to one embodiment of the present disclosure.

FIG. 16 is a flow diagram illustrating a method for operating an RFsystem according to one embodiment of the present disclosure.

FIGS. 17A and 17B are graphs illustrating a non-linear function for usein an RF system according to various embodiments of the presentdisclosure.

FIG. 18 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 19 is a functional schematic illustrating an RF system according toone embodiment of the present disclosure.

FIG. 20 is a functional schematic illustrating intelligent bridgecircuitry according to one embodiment of the present disclosure.

FIG. 21 is a functional schematic illustrating envelope tracking powersupply circuitry according to one embodiment of the present disclosure.

FIG. 22 is a functional schematic illustrating transceiver circuitryaccording to one embodiment of the present disclosure.

FIG. 23 is a graph illustrating a magnitude of adjustment of a targetsupply voltage according to one embodiment of the present disclosure.

FIG. 24 is a graph illustrating a gain correction adjustment value to beused in an RF system according to one embodiment of the presentdisclosure.

FIG. 25 is a graph illustrating a phase adjustment value to be used inan RF system according to one embodiment of the present disclosure.

FIG. 26 is a flow diagram illustrating a method for operating an RFsystem according to one embodiment of the present disclosure.

FIG. 27 is a functional schematic illustrating an equivalent circuit forone or more RF power amplifiers according to one embodiment of thepresent disclosure.

FIG. 28 is a functional schematic illustrating envelope tracking powersupply circuitry according to one embodiment of the present disclosure.

FIG. 29 is a functional schematic illustrating envelope tracking powersupply circuitry according to one embodiment of the present disclosure.

FIG. 30 is a flow diagram illustrating a method for operating an RFsystem according to one embodiment of the present disclosure.

FIG. 31 is a functional schematic illustrating envelope synchronizationcircuitry according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Embodiments are described herein with reference to schematicillustrations of embodiments of the disclosure. As such, the actualdimensions of the layers and elements can be different, and variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are expected. For example, aregion illustrated or described as square or rectangular can haverounded or curved features, and regions shown as straight lines may havesome irregularity. Thus, the regions illustrated in the figures areschematic and their shapes are not intended to illustrate the preciseshape of a region of a device and are not intended to limit the scope ofthe disclosure. Additionally, sizes of structures or regions may beexaggerated relative to other structures or regions for illustrativepurposes and, thus, are provided to illustrate the general structures ofthe present subject matter and may or may not be drawn to scale. Commonelements between figures may be shown herein with common element numbersand may not be subsequently re-described.

FIG. 1 is a functional schematic illustrating a radio frequency (RF)system 10 according to one embodiment of the present disclosure. The RFsystem 10 includes one or more RF power amplifiers 12, transceivercircuitry 14, and envelope tracking modulator circuitry 16. The one ormore RF power amplifiers 12 are coupled between the transceivercircuitry 14 and an RF output 18, which may be coupled to one or moreantennas (not shown). The envelope tracking modulator circuitry 16 iscoupled between the transceiver circuitry 14 and the one or more RFpower amplifiers 12. In particular, the envelope tracking modulatorcircuitry 16 is coupled between envelope tracking support circuitry 20in the transceiver circuitry 14 and the one or more RF power amplifiers12.

In operation, the transceiver circuitry 14 is configured to receive abaseband input signal BB_(in) and modulate the baseband input signalBB_(in) to generate an RF input signal RF_(in), which is provided to theone or more RF power amplifiers 12. The envelope tracking supportcircuitry 20 in the transceiver circuitry 14 is configured to generate atarget supply voltage V_(t) based on the RF input signal RF_(in). Thetarget supply voltage V_(t) represents a target voltage to be providedto the one or more RF power amplifiers 12 that tracks a power envelopeof the RF input signal RF_(in) such that a desired headroom ismaintained when amplifying the RF input signal RF_(in), and is thereforeindicative of a power envelope of the RF input signal RF_(in). Theenvelope tracking modulator circuitry 16 receives the target supplyvoltage V_(t) and a supply voltage V_(supply), e.g., a battery voltage,and modulates the supply voltage V_(supply) based on the target supplyvoltage V_(t) to provide an envelope tracking supply voltage V_(cc). Inone embodiment, the envelope tracking modulator circuitry 16 performs asimple linear amplification of the target supply voltage V_(t) toprovide the envelope tracking supply voltage V_(cc). The one or more RFpower amplifiers 12 receive the RF input signal RF_(in) and the envelopetracking supply voltage V_(cc), and amplify the RF input signal RF_(in)using the envelope tracking supply voltage V_(cc) to provide an RFoutput signal RF_(out) at the RF output 18.

Those skilled in the art will appreciate that if the envelope trackingsupply voltage V_(cc) accurately tracks the power envelope of the RFoutput signal RF_(out), a constant headroom can be maintained whenamplifying the RF input signal RF_(in) that keeps the one or more RFpower amplifiers 12 operating at peak efficiency and/or linearity andthus improves the performance of the RF system 10. However, providingthe envelope tracking supply voltage V_(cc) in such a manner is oftenquite difficult. In the embodiment in FIG. 1, the envelope trackingsupport circuitry 20 in the transceiver circuitry 14 must provide thetarget supply voltage V_(t) such that the envelope tracking supplyvoltage V_(cc) and the power envelope of the RF output signal RF_(out)are synchronized in time. Often, this is quite difficult becausegenerating the target supply voltage V_(t) involves inherent delays thatcause the envelope tracking supply voltage V_(cc) to be out of sync withthe power envelope of the RF output signal RF_(out). In some situations,it may be desirable in many applications to reduce the complexity oftransceiver circuitry 14 and offload all or most of the envelopetracking functionality for an RF system 10 into a single component orchip. Further, some situations (e.g., fifth generation (5G) and mmWaveapplications) require the transceiver circuitry 14 to be located a longdistance from the one or more RF power amplifiers 12 and thus theenvelope tracking modulator circuitry 16, making it impractical toprovide the target voltage V_(t) from the envelope tracking supportcircuitry 20 to the envelope tracking modulator circuitry 16 as shown.

Accordingly, FIG. 2 shows the RF system 10 according to an additionalembodiment of the present disclosure. The RF system 10 shown in FIG. 2is substantially similar to that shown in FIG. 1, except that theenvelope tracking support circuitry 20 is removed from the transceivercircuitry 14 and additional functionality is added to the envelopetracking modulator circuitry 16 to provide envelope tracking powersupply circuitry 22. In particular, the envelope tracking power supplycircuitry 22 includes the envelope tracking modulator circuitry 16,power envelope detector circuitry 24, and a look up table (LUT) 26. Thepower envelope detector circuitry 24 is between a coupler 28 and the LUT26. The power envelope detector circuitry 24 is configured to measure apower envelope of the RF input signal RF_(in) provided from thetransceiver circuitry 14 to the one or more RF power amplifiers 12 viathe coupler 28, providing a power envelope measurement PE_(m) to the LUT26. The LUT 26 is between the power envelope detector circuitry 24 andthe envelope tracking modulator circuitry 16. The LUT 26 is configuredto look up a target supply voltage V_(t) based on the power envelopemeasurement PE_(m) via a known relationship between the power envelopemeasurement PE_(m) and the target supply voltage V_(t) for maintaining adesired efficiency and/or linearity of the one or more RF poweramplifiers 12. The target supply voltage V_(t) is provided to theenvelope tracking modulator circuitry 16. The envelope trackingmodulator circuitry 16 operates as described above, modulating thesupply voltage V_(supply) based on the target supply voltage V_(t) toprovide the envelope tracking supply voltage V_(cc) to the one or moreRF power amplifiers 12.

The RF system 10 shown in FIG. 2 has the advantage of providing allcircuitry necessary for envelope tracking in the envelope tracking powersupply circuitry 22, thereby allowing the transceiver 14 to beindependent of the envelope tracking functionality and thus notspecialized for any particular envelope tracking application. This maybe particularly useful in 5G or mmWave applications wherein thetransceiver 14 is located relatively far away from the envelope trackingpower supply circuitry 22, presenting challenges to the delivery of thetarget voltage V_(t) thereto.

As discussed above, the measurement of the power envelope of the RFinput signal RF_(in) will always have a delay associated with it,resulting in a delayed envelope tracking supply voltage V_(cc). This isillustrated in the graph in FIG. 3, which shows an exemplary RF signalRF_(s), an actual power envelope PE_(a) of the exemplary RF signalRF_(s), a measured power envelope PE_(m) of the exemplary RF signalRF_(s), and a target supply voltage V_(t) based on the measured powerenvelope PE_(m) as provided from the LUT 26. As shown, there is a delaydT₁ between the measured power envelope PE_(m) and the actual powerenvelope PE_(a) of the exemplary RF signal RF_(s), and an additionaldelay dT₂ between the measured power envelope PE_(m) and the targetsupply voltage V_(t). As shown in the right-hand portion of the drawing,this will cause compression and/or clipping of signals amplified by theone or more RF power amplifiers 12. It is therefore desirable tominimize delays between the envelope tracking supply voltage V_(cc) andthe actual power envelope PE_(a) of the exemplary RF signal RF_(s).

Those skilled in the art will appreciate that the target supply voltageV_(t) may be provided based on an isogain contour for the one or more RFpower amplifiers 12, where an isogain contour expresses a relationshipbetween the power envelope of RF signals amplified by the one or more RFpower amplifiers 12 and the envelope tracking supply voltage V_(cc) thatwill maximize the linearity and/or efficiency of the one or more RFpower amplifiers 12. The LUT 26 may thus provide the target supplyvoltage V_(t) based on an isogain contour for the one or more RF poweramplifiers 12. FIG. 4A is a graph illustrating an exemplary isogaincontour (solid line) according to one embodiment of the presentdisclosure. As shown, the isogain contour expresses a relationshipbetween the measured power envelope PE_(m) and the target supply voltageV_(t). Generally, providing the target supply voltage V_(t) based on theisogain contour will lead to maximum linearity of the one or more RFpower amplifiers 12.

However, as discussed above, due to delays in the measurement of thepower envelope and the resulting target supply voltage V_(t), simplyproviding the target supply voltage V_(t) according to the isogaincontour may lead to compression and/or clipping. One way to avoid theseissues is to change a slope adjustment value, referred to herein as K,of the isogain contour depending on the amount of delay between theactual power envelope of an RF signal, the measured power envelopethereof, and the resulting envelope tracking supply voltage. As shown bythe dashed lines in FIG. 4A, K can be varied from zero, resulting in theisogain contour itself, to one, which results in a straight horizontalline, such that a higher K results in a reduced slope of the isogaincontour. FIG. 4B illustrates how changing K affects the resultingenvelope tracking supply voltage V_(cc). A solid line in FIG. 4Billustrates an ideal envelope tracking supply voltage V_(cc) having nodelay with respect to the power envelope of an RF signal. A first dashedline marked with K=0 illustrates the actual envelope tracking supplyvoltage V_(cc) produced when the target supply voltage V_(t) is providedas discussed above according to the isogain contour. As shown, theactual envelope tracking supply voltage V_(cc) is significantly delayedwith respect to the ideal envelope tracking supply voltage V_(cc).Additional dashed lines marked 0<K<1 illustrate the effect of increasingthe slope adjustment value K of the isogain contour, resulting in lessaccurate envelope tracking, but also less clipping between the idealenvelope tracking supply voltage V_(cc) and the actual envelope trackingsupply voltage V_(cc). When K reaches one as illustrated by the dashedline marked K=1, the envelope tracking supply voltage V_(cc) is providedas a constant value no matter the power envelope of the RF signal,resulting in average power tracking (no envelope tracking).

While adjusting the slope adjustment value K of the isogain contour toprovide the target supply voltage V_(t) can thus be used to reduce oreliminate clipping, it comes at the cost of reduced efficiency due tothe unnecessarily high headroom provided. Similar to the approachdiscussed above, FIG. 5 is a graph illustrating another way in which anisogain contour can be modified using both the slope adjustment value Kand a maximum expected voltage V_(cc(max)) to provide different targetsupply voltages V_(t), where V_(cc(max)) is an expected maximum voltagefor the power envelope of an RF signal within a given period of time(e.g., a timeslot or signal transmission). By adjusting the isogaincontour based on the expected maximum voltage V_(cc(max)) and using theslope adjustment value K to compensate for delay, clipping may beavoided while slightly improving efficiency. However, there is still alarge amount of unnecessary headroom provided.

The LUT 26 may be reprogrammed with a particular slope adjustment valueK and/or expected maximum voltage V_(cc(max)) to reduce clipping.However, it would be desirable to modulate the slope adjustment value Kin real time to better track the actual power envelope of an RF signal.Referring back to FIG. 4B, it can be seen that while increasing theslope adjustment value K results in reduced and even eliminated clippingon each rising edge of the ideal envelope tracking supply voltageV_(cc), larger slope adjustment values K result in even less accuratetracking on each falling edge of the ideal envelope tracking supplyvoltage V_(cc), as there is significant overshoot. If the slopeadjustment value K can be modulated continuously, accurate envelopetracking can be achieved as discussed below.

FIG. 6 is thus a graph illustrating the effect of dynamically modulatingthe slope adjustment value K according to one embodiment of the presentdisclosure. In particular, FIG. 6 once again shows an ideal envelopetracking supply voltage V_(cc) (solid line) and an actual envelopetracking supply voltage V_(cc) (dashed line) where the slope adjustmentvalue K is zero. As shown, there is a significant delay between theideal envelope tracking supply voltage V_(cc) and the actual envelopetracking supply voltage V_(cc), which will result in clipping on therising edge thereof. An additional envelope tracking supply voltageV_(cc) (dotted line) is shown where the slope adjustment value K isdynamically modulated. In particular, on the rising edge of the signalthe slope adjustment value K is positively modulated, resulting inreduced slope of the isogain contour, and on the falling edge of thesignal the slope adjustment value K is negatively modulated, resultingin an increased slope of the isogain contour. This effectively advancesand delays the envelope tracking supply voltage V_(cc), allowing it toaccurately track the ideal response. As discussed in detail below, theslope adjustment value K can be dynamically modulated based on ameasured delay between the envelope tracking supply voltage V_(cc) andan actual power envelope of an RF signal.

FIG. 7 shows the RF system 10 according to an additional embodiment ofthe present disclosure. The RF system 10 shown in FIG. 7 issubstantially similar to that shown in FIG. 2, except that the envelopetracking power supply circuitry 22 further includes envelopesynchronization circuitry 30 and delay measurement circuitry 32. Theenvelope synchronization circuitry 30 is coupled between the LUT 26 andthe envelope tracking modulator circuitry 16. The delay measurementcircuitry 32 is coupled to the envelope synchronization circuitry 30.

In operation, the power envelope detector circuitry 24 operates asdiscussed above to measure the power envelope of the RF input signalRF_(in) and provide the power envelope measurement PE_(m). The LUT 26provides the target supply voltage V_(t) based on the power envelopemeasurement PE_(m). As discussed above, the LUT 26 may provide thetarget supply voltage V_(t) according to an isogain contour for the oneor more RF power amplifiers 12. The envelope synchronization circuitry30 receives the target supply voltage V_(t) and a delay measurementDEL_(m) from the delay measurement circuitry 32, where the delaymeasurement DEL_(m) is a measurement of the delay between the envelopetracking power supply signal V_(cc) and the power envelope of the RFinput signal RF_(in). There are many ways to measure the delay betweensignals, including both analog and digital approaches, all of which arecontemplated herein. The envelope synchronization circuitry 30determines an appropriate slope adjustment value K based on the delaymeasurement DEL_(m) and adjusts the target supply voltage V_(t) based onthe slope adjustment value K to provide an adjusted target supplyvoltage V_(ta). As discussed above, the slope adjustment value K affectsthe slope of the isogain contour and thus adjusting the target supplyvoltage V_(t) will effectively mean changing the slope or shape of theisogain contour from which the target supply voltage V_(t) is provided(see, e.g., FIGS. 4B and 5). As discussed above, the envelope trackingmodulator circuitry 16 modulates the supply voltage V_(supply) accordingto the adjusted target supply voltage V_(ta) to provide a compensatedenvelope tracking supply voltage V_(cc(comp)). Notably, the envelopesynchronization circuitry 30 operates continuously, adjusting the targetsupply voltage V_(t) based on the delay measurement DEL_(m) as itchanges to provide the adjusted target supply voltage V_(ta). Thisallows the compensated envelope tracking supply voltage V_(cc(comp)) tobe synchronized with the power envelope of the RF input signal.

Notably, the envelope tracking power supply circuitry 22 may be anintegrated circuit, providing an envelope tracking integrated circuit(ETIC). All of the functionality relating to envelope tracking isprovided in the envelope tracking power supply circuitry 22 as discussedabove, thereby removing any specialized requirements for the transceivercircuitry 14 and aggregating the envelope tracking functionality in asingle integrated circuit in some embodiments.

To better illustrate the concepts herein, Equation (1) expresses acompensated envelope tracking supply voltage V_(cc(comp))(t) as afunction of an actual envelope tracking supply voltage V_(cc)(t):

V _(cc(comp))(t)=V _(cc)(t)+K(t)×[V _(cc(max)) −V _(cc)(t)]  (1)

where, as discussed above, V_(cc(max)) is the maximum expected voltagefor the power envelope of an RF signal for a given period of time andK(t) is the slope adjustment value. V_(cc(max)) may be known ahead oftime for a given period of time (e.g., a time slot or symbol) and, inthe context of the envelope tracking power supply circuitry 22, may belooked up or otherwise estimated by the circuitry itself or communicatedto the circuitry, for example, from the transceiver circuitry 14 via acommunications mechanism such as an RF front end (RFFE) bus. Thoseskilled in the art will appreciate that the compensated envelopetracking supply voltage V_(cc(comp))(t) is directly related to theadjusted target supply voltage V_(ta) by a gain applied by the envelopetracking modulation circuitry 16. The equations herein discuss theeffect of the slope adjustment value K(t) directly on the compensatedenvelope tracking supply voltage V_(cc(comp))(t) for the sake ofsimplicity. The slope adjustment value K(t) can thus be expressedaccording to Equation (2):

$\begin{matrix}{{K(t)} = \frac{V_{c{c{({comp})}}} - {V_{cc}(t)}}{V_{{cc}{(\max)}} - {V_{cc}(t)}}} & (2)\end{matrix}$

As discussed above, the actual envelope tracking supply voltage V_(cc)is related to an ideal envelope tracking supply voltage V_(cc(ideal)) bya function of some delay dT, which may be equal to or otherwise relatedto the delay measurement DEL_(m), according to Equation (3):

V _(cc)(t)=V _(cc(ideal))(t−dT)  (3)

Ideally, the compensated envelope tracking supply voltage V_(cc(comp))will be equal to the ideal envelope tracking supply voltageV_(cc(ideal)). Accordingly, K(t) can be expressed as in Equation (4):

$\begin{matrix}{{K(t)} \cong \frac{{V_{c{c{({ideal})}}}(t)} - {V_{cc}(t)}}{{V_{{cc}{(\max)}}(t)} - {V_{cc}(t)}}} & (4)\end{matrix}$

since V_(cc(ideal))(t)=V_(cc)(t+dT), Equation (4) can be rewritten asEquation (5):

$\begin{matrix}{{{K(t)} \cong \frac{{V_{cc}( {t + {dT}} )} - {V_{cc}(t)}}{V_{{cc}{(\max)}} - {V_{cc}(t)}}} = \frac{\Delta{V_{cc_{dT}}(t)}}{V_{{cc}{(\max)}} - {V_{cc}(t)}}} & (5)\end{matrix}$

assuming V_(cc)(t+dT)−V_(cc)(t)≈V_(cc)(t)−V_(cc)(t−dT), K(t) can againbe rewritten according to equation (6):

$\begin{matrix}{{K(t)} = \frac{{V_{cc}(t)} - {V_{cc}( {t - {dT}} )}}{V_{{cc}{(\max)}} - {V_{cc}(t)}}} & (6)\end{matrix}$

The compensated envelope tracking supply voltage V_(cc(comp))(t) canthus be rewritten according to Equation (7):

$\begin{matrix}{{V_{c{c{({comp})}}}(t)} = {{V_{cc}(t)} + {\frac{{V_{cc}(t)} - {V_{cc}( {t - {dT}} )}}{V_{{cc}{(\max)}} - {V_{cc}(t)}} \times ( {V_{{cc}{(\max)}} - {V_{cc}(t)}} )}}} & (7)\end{matrix}$

which can be rewritten as Equation (8):

V _(cc(comp))(t)=V _(cc)(t)+(V _(cc)(t)−V _(cc)(t−dT))=V _(cc)(t)+ΔV_(cc) _(dT) (t)  (8)

where ΔV_(cc) _(dT) can be calculated directly as V_(cc)(t)−V_(cc)(t−dT)or as a derivative

$\begin{matrix}{\frac{d{V_{cc}(t)}}{dt}*d{T.}} & \;\end{matrix}$

As shown above the function of K(t) is essentially to time advance ortime delay the compensated envelope tracking supply voltageV_(cc(comp))(t) to compensate for delays and thus synchronize thecompensated envelope tracking supply voltage V_(cc(comp))(t) with theideal envelope tracking supply voltage V_(cc(ideal))(t) and thus thepower envelope of an RF signal. K(t) is a function of ΔV_(cc) _(dT) (t),where ΔV_(cc) _(dT) (t) may in some cases, i.e., those in which it isdesired to time advance V_(cc(comp))(t), be a value of the envelopetracking supply voltage V_(cc)(t) at some point in the future. Since itis not possible to actually predict the value of the envelope trackingsupply voltage V_(cc)(t) in the future, an estimation based on arelationship between the time advanced and time delayed version ofV_(cc)(t), i.e., V_(cc)(t+dT)−V_(cc)(t)≅V_(cc)(t)−V_(cc)(t−dT), may beused. However, this relationship may not be accurate in allcircumstances. Accordingly, a derivative of V_(cc)(t), e.g.,

$\begin{matrix}{{\frac{d{V_{cc}(t)}}{dt}*dT},} & \;\end{matrix}$

may be used to estimate the value of V_(cc)(t) in the future. In thecase where ΔV_(cc) _(dT) (t) is estimated using a derivative, this mayyield a value for K(t) resulting in a compensated envelope trackingsupply voltage V_(cc(comp))(t) that is too high with respect to theideal envelope tracking supply voltage V_(cc(ideal))(t), providingexcessive headroom that reduces efficiency, or too low with respect tothe ideal envelope tracking supply voltage V_(cc(ideal))(t), leading tocompression and/or clipping. For example, using the derivative tocalculate ΔV_(cc) _(dT) (t) can lead to constant undershoot or overshootof V_(cc(comp))(t) with respect to V_(cc(ideal))(t) as well asundershooting V_(cc(comp))(t) near troughs in V_(cc)(t) and overshootingV_(cc(comp))(t) near peaks in V_(cc)(t). To compensate for this fact,Equation (1) can be rewritten as Equation (9):

V _(cc(comp))(t)=V _(cc)(t)+K _(comp)(t)×[V _(cc(max)) −V _(cc)(t)]  (9)

where K_(comp)(t) is provided according to Equation (10):

$\begin{matrix}{{K_{comp}(t)} = {{K_{offset}( {dT} )} + {\frac{dV_{cc}}{dt}*dT*\frac{{NLG}( \frac{d{V_{cc}(t)}}{dt} )}{V_{{cc}{(\max)}} - {V_{cc}(t)}}}}} & (10)\end{matrix}$

where K_(offset)(dT) is a constant offset value and

$\begin{matrix}{{NLG}( \frac{d{V_{cc}(t)}}{dT} )} & \;\end{matrix}$

is a non-linear gain function. K_(offset)(dT) provides a static level ofcompensation for constant error present in K_(comp)(t) that results in acompensated envelope tracking supply voltage V_(cc(comp))(t) that isconsistently above or below the ideal envelope tracking supply voltageV_(cc(ideal))(t) by some amount. K_(offset)(dT) may be determined in afactory calibration process or pre-programmed.

$\begin{matrix}{{NLG}( \frac{d{V_{cc}(t)}}{dt} )} & \;\end{matrix}$

compensates for undershooting and overshooting at peaks and troughs ofV_(cc)(t) by applying a non-linear function to the derivative thereof,which may reduce gain near peaks and troughs in V_(cc)(t). Those skilledin the art will appreciate that any suitable non-linear function can beused to compensate for the undershooting and overshooting discussedherein. Notably, the delay dT may be negative or positive in any of theabove equations. K_(comp)(t) can be broken down into a linear componentand a non-linear component. The linear component K_(comp(linear))(t) isshown in Equation (11):

$\begin{matrix}{{K_{com{p{({linear})}}}(t)} = {{K_{offset}( {dT} )} + {\frac{d{V_{cc}(t)}}{dt}*\frac{dT}{V_{{cc}{(\max)}} - {V_{cc}(t)}}}}} & (11)\end{matrix}$

where K_(comp)(t), including both the linear component and thenon-linear component can be expressed according to Equation (12):

$\begin{matrix}{{K_{comp}(t)} = {{K_{com{p{({linear})}}}(t)}*{{NLG}( \frac{d{V_{cc}(t)}}{dt} )}}} & (12)\end{matrix}$

In some embodiments, K_(comp)(t) may always be a positive value, asshown in Equation (13):

$\begin{matrix}{{K_{comp}(t)} = | {{K_{offset}( {dT} )} + {\frac{d{V_{cc}(t)}}{dt}*dT*\frac{{NLG}( \frac{d{V_{cc}(t)}}{dt} )}{V_{{cc}{(\max)}} - {V_{cc}(t)}}}} |} & (13)\end{matrix}$

when K_(comp)(t) is always a positive value as shown in Equation (13),the compensated envelope tracking supply voltage V_(cc(comp)) may be“windowed” so that it can be either advanced or delayed with respect tothe uncompensated envelope tracking supply voltage V_(cc(actual)). Thecompensated envelope tracking supply voltage V_(cc(comp)) will always behigher than the uncompensated envelope tracking supply voltageV_(cc(actual)) to avoid clipping and thus distortion in the RF outputsignal RF_(out).

Notably, the RF system 10 shown in FIG. 7 may work similarly when thetransceiver circuitry 14 provides an intermediate frequency (IF) inputsignal IF_(in), such as in mmWave applications. Such an embodiment isshown in FIG. 8, which is substantially similar to FIG. 7 except thatupconverter circuitry 33 is coupled between the transceiver circuitry 14and the one or more RF power amplifiers 12. The upconverter circuitry 33upconverts the IF input signal W_(in) to the RF input signal RF_(in). Asshown, the envelope tracking power supply circuitry 22 uses the IF inputsignal IF_(in) to generate the compensated envelope tracking supplyvoltage V_(cc(comp)), however, the coupler 28 could also be moveddownstream from the upconverter circuitry 33 so that the RF input signalRF_(in) is used instead.

In some embodiments, the envelope tracking power supply circuitry 22 maybe configured to provide a first compensated envelope tracking supplyvoltage V_(cc(comp)1) to a first stage RF power amplifier 12A andprovide a second compensated envelope tracking supply voltageV_(cc(comp)2) to a second stage RF power amplifier 12B, as shown in FIG.9. To do so, the envelope synchronization circuitry 30 may generate andprovide a first adjusted target voltage V_(ta1) and a second adjustedtarget voltage V_(ta2) to the envelope tracking modulator circuitry 16,which modulates the supply voltage V_(supply) based on the firstadjusted target voltage V_(ta1) to provide the first compensatedenvelope tracking supply voltage V_(cc(comp)1) and modulates the supplyvoltage V_(supply) based on the second adjusted target voltage V_(ta2)to provide the second compensated envelope tracking supply voltageV_(cc(comp)2). The first adjusted target voltage V_(ta1) may be providedby adjusting the target voltage V_(t) by a first amount while the secondadjusted target voltage V_(ta2) may be adjusted by a second amount. Inparticular, the time delay or time advance applied to the first adjustedtarget voltage V_(ta1) may be different from the time delay or timeadvance applied to the second adjusted target voltage V_(ta2).Synchronization of the second compensated envelope tracking supplyvoltage V_(cc(comp)1) with the power envelope of the RF signal may bemore critical to the operation of the RF system 10 than synchronizationof the first compensated envelope tracking supply voltage V_(cc(comp)1),and thus the first adjusted target voltage V_(ta1) and the secondadjusted target voltage V_(ta2) may be provided accordingly.

FIG. 10 shows the RF system 10 according to an additional embodiment ofthe present disclosure. The RF system 10 shown in FIG. 10 issubstantially similar to that shown in FIG. 7, but further includes oneor more additional RF power amplifiers 34 and splitter circuitry 36coupled between the transceiver circuitry 14, the one or more RF poweramplifiers 12, and the one or more additional RF power amplifiers 34.The splitter circuitry 36 is configured to split the RF input signalRF_(in) into a first RF input signal RF_(in1) and a second RF inputsignal RF_(in2). The first RF input signal RF_(in1) is amplified asdiscussed above with the one or more RF power amplifiers 12 using afirst compensated envelope tracking supply voltage V_(cc(comp)1) asdiscussed above to provide a first RF output signal RF_(out1). Thesecond RF input signal RF_(in2) is similarly amplified using a secondcompensated envelope tracking supply voltage V_(cc(comp)2) to provide asecond RF output signal RF_(out2). The coupler 28 may be split into afirst coupler 28A for measuring the first RF input signal RF_(in1) and asecond coupler 28B for measuring the second RF input signal RF_(in2).

The envelope synchronization circuitry may be used in self-containedenvelope tracking power supply circuitry 22 as shown above with respectto FIGS. 7-10, or may be used along with transceiver circuitry 14including envelope tracking support circuitry 20. Accordingly FIG. 11shows the RF system 10 according to an additional embodiment of thepresent disclosure, showing details of the envelope tracking supportcircuitry 20. As shown, the transceiver circuitry 14 includes envelopetracking support circuitry 20, which as discussed above with respect toFIG. 1 provides the target voltage V_(t). In particular, the envelopetracking support circuitry 20 includes power envelope detector circuitry38, a LUT 40, and digital to analog converter (DAC) circuitry 42. Alsoshown the transceiver circuitry 14 includes modulator circuitry 44,which receives the baseband input signal BB_(in) and modulates thesignal to provide the RF input signal RF_(in). The power envelopedetector circuitry 38 is configured to generate a digital power envelopemeasurement signal PE_(m(d)) from the baseband input signal BB_(in). TheLUT 40 is configured to generate a digital target voltage V_(t(d)) basedon a look up of the digital power envelope measurement signal PE_(m(d)).The DAC circuitry 42 is configured to convert the digital target voltageV_(t(d)) to an analog signal, providing the target voltage V_(t). Thepower envelope detector 24, the LUT 26, and the coupler 28 are omittedfrom the envelope tracking power supply circuitry 22, and the targetvoltage V_(t) is provided directly to the envelope synchronizationcircuitry 30 from the envelope tracking support circuitry 20 in thetransceiver circuitry 14. The envelope synchronization circuitry 30operates in the same way described above to adjust the target voltageV_(t), providing the adjusted target voltage V_(ta) and thussynchronizing the compensated envelope tracking supply voltageV_(cc(comp)) with the power envelope of the RF signal.

In another embodiment, the envelope tracking support circuitry 20 in thetransceiver circuitry 14 may provide the power envelope measurementPE_(in) instead of the target voltage as shown in FIG. 12. In such anembodiment, the LUT 40 is omitted from the envelope tracking supportcircuitry 20 and the digital power envelope measurement PE_(m(d)) isprovided to the DAC circuitry 42. The DAC circuitry 42 converts thedigital power envelope measurement PE_(m(d)) to an analog signal,providing the power envelope measurement signal PE_(m) to the LUT 26 inthe envelope tracking power supply circuitry 22. The LUT 26 will performthe same function described above to provide the target voltage V_(t),for example, according to an isogain contour. The target voltage V_(t)is adjusted by the envelope synchronization circuitry 30 as discussedabove to provide the adjusted target supply voltage V_(ta), which isused to provide the compensated envelope tracking supply voltageV_(cc(comp)).

In yet another embodiment, the functionality of the envelopesynchronization circuitry 30 may be implemented in the envelope trackingsupport circuitry 20 as shown in FIG. 13. In such an embodiment, theenvelope tracking support circuitry 20 further includes envelopesynchronization circuitry 46 between the LUT 40 and the DAC circuitry42. The envelope synchronization circuitry 46 in the envelope trackingsupport circuitry 20 operates in the same manner as described above withrespect to the envelope synchronization circuitry 30 in the envelopetracking power supply circuitry 22. However, the same operations may beperformed in the digital domain rather than the analog domain. Theenvelope synchronization circuitry 46 thus receives the digital targetvoltage V_(t(d)) and provides a digital adjusted target voltageV_(ta(d)). The digital adjusted target voltage V_(ta(d)) is provided tothe DAC circuitry 42, where it is converted to an analog signal as theadjusted target voltage V_(ta), which is provided directly to theenvelope tracking modulator circuitry 16. The envelope trackingmodulator circuitry 16 operates as described above to provide thecompensated envelope tracking supply voltage V_(cc(comp)) based on theadjusted target voltage V_(ta).

In general, the synchronization techniques discussed herein can beimplemented solely in the transceiver circuitry 14, solely in theenvelope tracking power supply circuitry 22, or distributed across thetransceiver circuitry 14, the envelope tracking power supply circuitry22, or any other circuitry.

FIG. 14 is a graph illustrating an exemplary RF signal RF_(s), an actualpower envelope PE_(a) of the exemplary RF signal RF_(s), anuncompensated envelope tracking supply voltage V_(cc(actual)), and acompensated envelope tracking supply voltage V_(cc(comp)). As shown, theuncompensated envelope tracking supply voltage V_(cc(actual)) is delayedwith respect to the actual power envelope PE_(a) of the exemplary RFsignal RF_(s) such that clipping results. The compensated envelopetracking supply voltage V_(cc(comp)), which is generated according tothe principles discussed herein, accurately tracks the actual powerenvelope PE_(a) of the exemplary RF signal RF_(s) with sufficientheadroom to maintain linearity and efficiency. As shown, the compensatedenvelope tracking supply voltage V_(cc(comp)) is effectivelytime-advanced with respect to the uncompensated envelope tracking supplyvoltage V_(cc(actual)) by the time delay dT.

As discussed above, the compensated envelope tracking supply voltageV_(cc(comp)) may sometimes be time-advanced with respect to theuncompensated envelope tracking supply voltage V_(cc(actual)), but alsomay be time-delayed with respect to the uncompensated envelope trackingsupply voltage V_(cc(actual)) FIG. 15 is a graph illustrating theuncompensated envelope tracking supply voltage V_(cc(actual)), atime-advanced envelope tracking supply voltage V_(cc(advanced)), and atime-delayed envelope tracking supply voltage V_(cc(delayed)). Theresulting compensated envelope tracking supply voltage V_(cc(comp)) maybe the maximum of the uncompensated envelope tracking supply voltageV_(cc(actual)), the time-advanced envelope tracking supply voltageV_(cc(advanced)), and the time-delayed envelope tracking supply voltageV_(cc(delayed)). The equations discussed above provide the compensatedenvelope tracking supply voltage V_(cc(comp)) to meet this criteria.However, the compensated envelope tracking supply voltage V_(cc(comp))may also be obtained by separately generating the time-advanced envelopetracking supply voltage V_(cc(advanced)) and the time-delayed envelopetracking supply voltage V_(cc(delayed)) according to the methodsdescribed above, then taking the maximum thereof.

FIG. 16 is a flow diagram illustrating a method for providing anenvelope tracking supply voltage according to one embodiment of thepresent disclosure. First, a power envelope measurement is received(step 100). As discussed above, the power envelope measurement may bereceived via a coupler and measured by power envelope detectorcircuitry. Alternatively, the power envelope measurement may beperformed digitally in transceiver circuitry. A target supply voltage isthen determined based on the power envelope measurement (step 102). Asdiscussed above, the target supply voltage may be determined based on alook up in a LUT, which may be provided according to an isogain contourfor an RF power amplifier. Further as discussed above, the target supplyvoltage may be delayed with respect to an ideal supply voltage.Accordingly, the target supply voltage is adjusted based on a delaymeasurement (step 104), where the delay measurement indicates an amountof delay between the power envelope of an RF signal and the envelopetracking supply voltage. As discussed above, the target supply voltagemay be adjusted by envelope synchronization circuitry. The envelopetracking supply voltage is then generated based on the adjusted targetsupply voltage (step 106), e.g., via envelope tracking modulatorcircuitry. Details regarding each of the steps, and, in particular, howthe target supply voltage is adjusted to provide the adjusted targetsupply voltage, are discussed above (see, e.g., Equations 1-13).

As discussed above with respect to Equations 10, 12, and 13, anon-linear gain function is used so to prevent overshooting at peaks ofV_(cc(comp))(t). In particular,

$\begin{matrix}{{NLG}( \frac{d{V_{cc}(t)}}{dt} )} & \;\end{matrix}$

compensates for undershooting and overshooting at peaks and troughs ofV_(cc(comp))(t) by applying a non-linear function to the derivativethereof, which may reduce gain near peaks and troughs inV_(cc(comp))(t). FIG. 17A is a graph illustrating one example of thenon-linear gain function

$\begin{matrix}{{{NLG}( \frac{d{V_{cc}(t)}}{dt} )}.} & \;\end{matrix}$

FIG. 17A shows a graph of gain vs a normalized derivative of V_(cc)(t).The non-linear gain function can be expressed according to Equation(15):

$\begin{matrix}{{{NLG}( \frac{d{V_{cc}(t)}}{dt} )} = | {\frac{\frac{{dV}_{cc}(t)}{dt}}{\frac{d{V_{{cc}{(\max)}}(t)}}{dt} - N_{offset}}*N_{comp}} \middle| {*1.0} } & (15)\end{matrix}$

where N_(offset) is a static value that can be changed to offset wherethe valley in the function shown in FIG. 17A occurs and N_(comp) is astatic value that can be changed to determine how much non-linearity isapplied. FIG. 17A shows the non-linear gain function with N_(offset)=0and N_(comp)=4. Generally, overshooting at peaks of V_(cc)(t) is muchmore of a problem than undershooting at valleys, and so it may bebeneficial to provide the non-linear gain function as shown in FIG. 17B,wherein N_(offset)=0.08 and N_(comp)=4. As shown, the non-linear gainfunction is offset from zero so that more compensation is provided whenthe derivative is positive (approaching a peak) rather than negative(approaching a valley). This may further reduce overshooting at peaks ofV_(cc)(t). Those skilled in the art will appreciate that the non-lineargain function shown in FIGS. 17A and 17B and discussed above is one ofmany possibilities for reducing overshooting at peaks ofV_(cc(comp))(t), and that the present disclosure contemplates the use ofany and all non-linear gain functions for accomplishing theseobjectives.

As discussed above, the improvements to the envelope tracking powersupply circuitry 22 discussed herein allow for a self-contained envelopetracking solution that requires no specialization of the transceivercircuitry 14. The transceiver circuitry 14, which may also be referredto as baseband circuitry or modem circuitry, is conventionally thecontrol center of the RF system, communicating with various partsthereof via a serial bus, such as an RF front end (RFFE) bus to programthe parts for timing and synchronization with slot and/or symbolboundaries or the like. Current trends in transceiver circuitry 14continue to see increases in the complexity thereof, with additionalfunctionality in the RF system being provided at least in part by thetransceiver circuitry 14. Accordingly, the demands on the transceivercircuitry 14 continue to increase and may become difficult to satisfy insome scenarios.

FIG. 18 shows the RF system 10 according to an additional embodiment ofthe present disclosure. In the RF system 10 shown in FIG. 18, the one ormore RF power amplifiers 12 are shown as one or more splitter, poweramplifier, duplexer (SPAD) blocks 46 coupled to the transceivercircuitry 14. As indicated by the name, each one of the SPAD blocks 46may include one or more splitters, RF power amplifiers, and duplexers.The envelope tracking power supply circuitry 22 is coupled to each oneof the SPAD blocks 46 to provide the compensated envelope trackingsupply voltage V_(cc(comp)) as discussed above. Coupler circuitry 48 iscoupled to the output of the one or more SPAD blocks 46. One or moreantenna tuners 50 are coupled between the coupler circuitry 48 and theRF output. In operation, the one or more SPAD blocks 46 receive the RFinput signal RF_(in), which may be split into one or more sub-signalsand amplified, before sending the amplified RF signals to the couplercircuitry 48. The coupler circuitry 48 may combine one or moreseparately amplified RF signals into a single RF output signal RF_(out).The one or more antenna tuners 50 tune the impedance or other operatingparameters of one or more connected antennas (not shown) for optimaltransmission. The one or more SPAD blocks 46, the coupler circuitry 48,and the one or more antenna tuners 50 may be provided in what isreferred to as an RF signal path. These and any other components in theRF signal path may be referred to as RF path components.

As shown, the transceiver circuitry 14 includes an RFFE bus connection52 coupled to an RFFE bus 54. Each one of the envelope tracking powersupply circuitry 22, the one or more SPAD blocks 46, the couplercircuitry 48, and the one or more antenna tuners 50 also includes anRFFE bus connection 52 coupled to the RFFE bus 54. The transceivercircuitry 14 communicates with the network to receive networkinformation such as band or sub-band information, transmission modes ofoperation, modulation type and bandwidth, etc. The transceiver circuitry14 uses this information to set one or more operating parameters of theone or more SPAD blocks 46, the coupler circuitry 48, and the one ormore antenna tuners 50 by sending information via the RFFE bus 54. Thetransceiver circuitry 14 may also send relevant information to theenvelope tracking power supply circuitry 22 via the RFFE bus 54, such asthe maximum expected voltage for a given symbol or slot V_(cc(max)) asdiscussed above, or any other relevant information that may then be usedby the envelope tracking power supply circuitry 22 to generate thecompensated envelope tracking supply voltage V_(cc(comp)).

FIG. 19 shows the RF system 10 according to an additional embodiment ofthe present disclosure. The RF system 10 shown in FIG. 19 issubstantially similar to that shown in FIG. 18, but further includesintelligent bridge circuitry 56. The intelligent bridge circuitry 56includes an RFFE bus connection 52, and is coupled to the transceivercircuitry 14 via the RFFE bus 54. Further, the intelligent bridgecircuitry 56 includes a secondary communications connection 58, such asone suitable for a single-wire communications bus (e.g., SμBUS). Thesecondary communications connection 58 is coupled to a secondarycommunications bus 60. Notably, each one of the envelope tracking powersupply circuitry 22, the one or more SPAD blocks 46, the couplercircuitry 48, and the one or more antenna tuners 50 include a secondarycommunications connection 58 which is coupled to the secondarycommunications bus 60.

In operation, the transceiver circuitry 14 continues to operate asdescribed above, communicating via the RFFE bus 54 to set one or moreoperating parameters of the one or more SPAD blocks 46, the couplercircuitry 48, the one or more antenna tuners 50, or any other circuitrynot shown based on network operating conditions such as band or sub-bandinformation, transmission modes of operation, modulation type andbandwidth, etc. The intelligent bridge circuitry 56 may separatelycommunicate with the one or more SPAD blocks 46, the coupler circuitry48, the one or more antenna tuners 50, the envelope tracking powersupply circuitry 22, or any other circuitry via the secondarycommunications bus 60 in order to alter or set one or more operatingparameters thereof based on other operating concerns such as envelopetracking modes of operation or the like. Providing the intelligentbridge circuitry 56 allows for the coordinated operation of the variouscomponents within the RF system 10 for additional modes of operationand/or improved performance without making any changes to thetransceiver circuitry 14, and thus may be advantageous in somesituations.

FIG. 20 shows details of the intelligent bridge circuitry 56 accordingto one embodiment of the present disclosure. The intelligent bridgecircuitry 56 includes processing circuitry 62, a memory 64, andcommunications circuitry 66. The memory 64 may store instructions,which, when executed by the processing circuitry 62 cause theintelligent bridge circuitry 56 to perform the functionality discussedabove. The communications circuitry 66 may include severalcommunications interfaces such as the RFFE connection 52 and thesecondary communications connection 58. In certain embodiments, theintelligent bridge circuitry 56 may be integrated into the envelopetracking power supply circuitry 22.

FIG. 21 shows details of the envelope tracking power supply circuitry 22according to one embodiment of the present disclosure. The envelopetracking power supply circuitry 22 is similar to that discussed above,but further includes processing circuitry 68, a memory 70,communications circuitry 72, and calibration circuitry 74. Theprocessing circuitry 68 may be coupled to each functional block in theenvelope tracking power supply circuitry 22 in order to coordinate theoperation thereof. The memory 70 may store instructions, which, whenexecuted by the processing circuitry 68, cause the envelope trackingcircuitry 22 to provide the functionality discussed herein. The memory70 may also store various tables and settings for different modes andbands of operations for the envelope tracking power supply circuitry 22,including look up tables for factory calibration and the like. Thecommunications circuitry 72 may include any number of communicationsinterfaces (e.g., for RFFE communications buses, single wirecommunications busses such as SμBUS, or the like) and thus may send andreceive information to/from other devices in the RF system 10. Thecalibration circuitry 74 may be configured to locally generate an RFpulsed continuous wave (CW) signal or any other suitable calibrationsignal, which is injected into the path of the one or more RF poweramplifiers 10 via the RF coupler 28. The response can then be measured(e.g., via measurement circuitry such as the RF coupler 28, anadditional coupler not shown, or any other suitable circuitry) togenerate the LUT 26 or any other operating parameters such that thecalibration of the envelope tracking power supply circuitry 22 can becompletely self-contained. The processing circuitry 68 may coordinatethis calibration process. Notably, the envelope tracking power supplycircuitry 22 shown in FIG. 21 may be used in any of the embodimentsdiscussed herein.

While providing the compensated envelope tracking supply voltageV_(cc(comp)) as described above results in synchronization with thepower envelope of the RF signal, the adjustments made to the targetsupply voltage V_(t) to accomplish this may mean that the adjustedtarget voltage V_(ta) no longer tracks an isogain contour for the one ormore RF power amplifiers 12. As discussed above, providing the targetvoltage V_(t) and thus envelope tracking supply voltage V_(cc) accordingto an isogain contour results in increased linearity and/or efficiencyof the one or more RF power amplifiers 12. The deviations in theadjusted target voltage V_(ta) from the isogain contour may result indistortion in the RF output signal RF_(out).

One way to solve this problem is by pre-distorting the RF input signalRF_(in) to offset the effects of the adjusted target voltage V_(ta) onthe RF output signal RF_(out). FIG. 22 thus shows the transceivercircuitry 14 according to one embodiment of the present disclosure. Inaddition to the parts discussed above, the transceiver circuitry 14further includes digital predistortion (DPD) circuitry 76 coupled to themodulator circuitry 44. The DPD circuitry 76 provides somepre-distortion of the baseband input signal BB_(in), which may be, forexample, an in-phase/quadrature (I/O) signal, to provide a pre-distortedbaseband input signal BB_(in(pd)). As shown, the DPD circuitry 76 maygenerate the pre-distorted baseband input signal BB_(in(pd)) based onthe digital adjusted target voltage V_(ta(d)) and a signal indicative ofthe power envelope of the baseband input signal BB_(in), which is shownin the present embodiment as an index i associated with the currentvalue for the digital power envelope measurement PE_(m(d)) in the LUT40. Notably, the index i is only one exemplary input, and any signalindicative of the power envelope of the baseband input signal BB_(in)may be used. The modulator 44 modulates the pre-distorted baseband inputsignal BB_(in(pd)) to provide the RF input signal RF_(in). The DACcircuitry 42 is shown optionally coupled to a number of different pointsin the envelope tracking support circuitry 20 such that it receives oneof the digital target voltage V_(t(d)), the digital power envelopemeasurement PE_(m(d)), and the digital adjusted target voltage V_(ta(d))and converts the received signal to an analog signal to provide one ofthe target voltage V_(t), the power envelope measurement PE_(m), and theadjusted target voltage V_(ta) to the envelope tracking power supplycircuitry 22. Conventionally, the pre-distortion applied by the DPDcircuitry 76 is used to offset the effects of using isogain to providethe target voltage V_(t) on the RF output signal RF_(out) (discussed indetail below). However, because the adjusted target voltage V_(ta) nolonger tracks the isogain contour for the one or more RF poweramplifiers 12, there will be distortion in the RF output signalRF_(out). Accordingly, the DPD circuitry 76 must provide additionalpre-distortion on the baseband input signal BB_(in).

The digital pre-distortion provided by the DPD circuitry 76 may beexpressed according to Equation (16):

G _(dpd) =G _(dpd(isogain)) *G _(dpd(ΔV) _(cc))   (14)

where G_(dpd) is the overall gain correction of the DPD circuitry 76,G_(dpd(isogain)) is the gain correction of the DPD circuitry 76configured to cancel distortion caused by the use of isogain with theone or more RF power amplifiers 12, and G_(dpd(ΔV) _(cc) ₎ is the gaincorrection of the DPD circuitry 76 configured to cancel the effect ofthe adjustments made to the adjusted target voltage V_(ta) that causedeviations from the isogain contours for the one or more RF poweramplifiers 12. Each of the gain correction terms discussed above iscomplex, including both amplitude and phase components.

Those skilled in the art will appreciate that G_(dpd(isogain)) isconventionally the only gain correction provided by the DPD circuitry76. The effect of G_(dpd(isogain)) is to counter the distortion causedby the use of isogain with the one or more RF power amplifiers 12.Referring back to FIG. 4A, the isogain contours shown are not linear,meaning that as the magnitude of the power envelope of an RF signalincreases, the target voltage V_(t) increases according to the shape ofthe curve shown. This will cause distortion in the RF output signalRF_(out), which can be cancelled by shaping the baseband input signalBB_(in) in an opposite fashion. As discussed above, because theadjustments made to the adjusted target voltage V_(ta) to synchronizethe compensated envelope tracking supply voltage V_(cc(comp)) with thepower envelope of the RF signal, simply using G_(dpd(isogain)) will nolonger cancel the distortion in the RF output signal RF_(out). Detailsof how G_(dpd(isogain)) is provided will be appreciated by those skilledin the art and thus are not discussed herein.

FIG. 23 is a graph illustrating ΔV_(cc) over time for a given envelopetracking power supply signal, where ΔV_(cc)(t)=V_(ta)(t)−V_(t)(t), orthe difference between the adjusted target voltage V_(ta) and the targetvoltage V_(t). As shown, ΔV_(cc) varies between 0 and 1 over time, andis indicative of the amount of deviation from the isogain curve that isoccurring at any moment.

FIG. 24 is a graph illustrating an amplitude correction component forG_(dpd(ΔV) _(cc) ₎ according to one embodiment of the presentdisclosure. The graph shows a relationship between gain applied andinput power of the baseband input signal BB_(in). Notably, several gaincurves are illustrated, each of which represents a different ΔV_(cc)value, where ΔV_(cc)(t)=V_(ta)(t)−V_(t)(t). Depending on the differencebetween the adjusted target voltage V_(ta) and the target voltage V_(t)at a given time, the gain curve used for G_(dpd(ΔV) _(cc) ₎ will bechosen as shown. The amplitude correction portion of G_(dpd(ΔV) _(cc) ₎can be expressed as a linear term, a second order equation, or a thirdorder equation, depending on a desired system complexity and accuracy ofgain correction, as shown in Equations (17), (18), and (19),respectively:

Gain_(ΔV) _(cc) (i,ΔV _(cc))=a(i)*ΔV _(cc)  (17)

Gain_(ΔV) _(cc) (i,ΔV _(cc))=a(i)*ΔV _(cc) +b(i)*ΔV _(cc) ²  (18)

Gain_(ΔV) _(cc) (i,ΔV _(cc))=a(i)*ΔV _(cc) +b(i)*ΔV _(cc) ² +c(i)*ΔV_(cc) ²  (19)

where a(i), b(i), and c(i) are polynomial coefficients that can bepre-programmed (e.g., by the characterization of a number of RF systems10) or extracted during calibration of each RF system 10. In someembodiments, the polynomial coefficients may be stored in a LUT. Whilethe amplitude correction function is shown as being dependent on theindex value i from the LUT 40, which as discussed above is indicative ofthe power envelope of the baseband input signal BB_(in), any signalindicative of the power envelope of the baseband input signal BB_(in)could be used in place of the index value i.

FIG. 25 is a graph illustrating a phase correction component forG_(dpd(ΔV) _(cc) ₎ according to one embodiment of the presentdisclosure. The graph shows a relationship between phase rotation andinput power of the baseband input signal BB_(in). Notably, several phasecorrection curves are illustrated, each of which represents a differentΔV_(cc) value, where ΔV_(cc)(t)=V_(ta)(t)−V_(t)(t). Depending on thedifference between the adjusted target voltage V_(ta) and the targetvoltage V_(t) at a given time, the phase correction curve used forG_(dpd(ΔV) _(cc) ₎ will be chosen as shown. The phase correction portionof G_(dpd(ΔV) _(cc) ₎ can be expressed as a linear term, a second orderequation, or a third order equation, depending on a desired systemcomplexity and accuracy of phase correction, as shown in Equations (20),(21), and (22), respectively:

Phase_(ΔV) _(cc) (i,ΔV _(cc))=d(i)*ΔV _(cc)  (20)

Phase_(ΔV) _(cc) (i,ΔV _(cc))=d(i)*ΔV _(cc) +e(i)*ΔV _(cc) ²  (21)

Phase_(ΔV) _(cc) (i,ΔV _(cc))=d(i)*ΔV _(cc) +e(i)*ΔV _(cc) ² +f(i)*ΔV_(cc) ²  (22)

where d(i), e(i), and f(i) are polynomial coefficients that can bepre-programmed (e.g., by the characterization of a number of RF systems10) or extracted during calibration of each RF system 10. In someembodiments, the polynomial coefficients may be stored in a LUT. Whilethe phase correction function is shown as being dependent on the indexvalue i from the LUT 40, which as discussed above is indicative of thepower envelope of the baseband input signal BB_(in), any signalindicative of the power envelope of the baseband input signal BB_(in)could be used in place of the index value i.

In general, the present disclosure contemplates generating predistortionfor an RF input signal RF_(in) based on an adjusted target voltageV_(ta) which has been adjusted to be synchronized in time with the powerenvelope of an RF signal. The foregoing discussion shows an exemplaryway to accomplish this task, but any suitable systems and methods may beused to accomplish these objectives. FIG. 26 is a flow diagramillustrating a method for operating an RF system 10 according to oneembodiment of the present disclosure. First, a power envelopemeasurement is received (step 200). As discussed above, the powerenvelope measurement may be received via a coupler and measured by powerenvelope detector circuitry. Alternatively, the power envelopemeasurement may be performed digitally in transceiver circuitry. Atarget supply voltage is then determined based on the power envelopemeasurement (step 202). As discussed above, the target supply voltagemay be determined based on a look up in a LUT, which may be providedaccording to an isogain contour for an RF power amplifier. Further asdiscussed above, the target supply voltage may be delayed with respectto an ideal supply voltage. Accordingly, the target supply voltage isadjusted based on a delay measurement (step 204), where the delaymeasurement indicates an amount of delay between the power envelope ofan RF signal and the envelope tracking supply voltage. As discussedabove, the target supply voltage may be adjusted by envelopesynchronization circuitry. The envelope tracking supply voltage is thengenerated based on the adjusted target supply voltage (step 206), e.g.,via envelope tracking modulator circuitry. Details regarding each of thesteps, and in particular how the target supply voltage is adjusted toprovide the adjusted target supply voltage, are discussed above (see,e.g., Equations 1-13). In addition to the above, an RF input signal maybe pre-distorted (e.g., digitally by DPD circuitry) to cancel the effectof adjusting the target supply voltage on the RF output signal (step208). This may be accomplished as described above.

The discussion up to this point has neglected the effects of theimpedance presented to the envelope tracking power supply circuitry 22from the one or more RF power amplifiers 12 on the compensated envelopetracking supply voltage V_(cc(comp)). However, those skilled in the artwill appreciate that the one or more RF power amplifiers 12 present animpedance to the envelope tracking power supply circuitry 22 that mayaffect the operation thereof. FIG. 27 illustrates an equivalent circuitfor the one or more RF power amplifiers 12 according to one embodimentof the present disclosure. As shown, the one or more RF power amplifiers12 can be represented by a voltage source, which provides thecompensated envelope tracking supply voltage V_(cc(comp)), a seriesinductor L, a shunt capacitance C, and a current source representing asupply current I_(cc) flowing from the envelope tracking power supplycircuitry 22 to the one or more RF power amplifiers 12. Notably, thesupply current I_(cc) is dependent on the RF input signal RF_(in), whichvaries over time. In particular, the supply current I_(cc) may berepresented by the power envelope measurement divided by some resistancePE_(m)/R or the target voltage divided by some resistance V_(t)/R.Because of the impedance from the series inductor L and the shuntcapacitor C, the supply current I_(cc) will generate an undesiredvoltage across the one or more RF power amplifiers 12. This undesiredvoltage is referred to herein as a source impedance voltage, and mayreduce headroom provided by the compensated envelope tracking supplyvoltage V_(cc(comp)) resulting in compression or clipping, or mayotherwise interfere with the operation of the envelope tracking powersupply circuitry 22.

One way to mitigate the aforementioned problems includes providingequalization to the target supply voltage V_(t) before modulation by theenvelope modulator circuitry 16 in order to reduce or eliminate thesource impedance voltage. Referring back to FIG. 7, in the case thatequalization is applied to the target supply voltage V_(t) before it isprovided to the envelope synchronization circuitry 30, the equalizationmay affect the functionality of the envelope synchronization circuitry30 discussed above such that the adjusted target supply voltage V_(ta)no longer accurately tracks the power envelope of the RF input signalRF_(in). In the case that equalization is applied to the adjusted targetsupply voltage V_(ta) before it is provided to the envelope modulatorcircuitry 16, the adjustments made by the envelope synchronizationcircuitry 30 will make it difficult if not impossible to cancel thesource impedance voltage, since the envelope synchronization circuitry30 has effectively delayed or advanced the target supply voltage V_(t)as discussed above such that it is no longer related to the RF inputsignal RF_(in) as normally expected.

To solve these problems, the envelope tracking power supply circuitry 22shown in FIG. 28 further includes impedance compensation circuitry 78,equalizer circuitry 80, and adder circuitry 82. The impedancecompensation circuitry 78 is configured to receive the power envelopemeasurement PE_(m) or the target voltage V_(t). Since the power envelopemeasurement PE_(m) may be provided by the envelope tracking supportcircuitry 20 in the transceiver circuitry 14 or the power envelopedetector circuitry 24, the impedance compensation circuitry 78 may becoupled to either of these parts accordingly. Similarly, since thetarget voltage V_(t) can be provided by the envelope tracking supportcircuitry 20 in the transceiver circuitry 14 or the LUT 26, theimpedance compensation circuitry 78 may be coupled to either of theseparts accordingly. The equalizer circuitry 80 is coupled between theenvelope synchronization circuitry 30 and the adder circuitry 82. Inoperation, the power envelope detector 24, the LUT 26, the envelopesynchronization circuitry 30, and the delay measurement circuitry 32behave as described above. The impedance compensation circuitry 78receives the power envelope measurement PE_(m) or the target voltageV_(t) and provides an impedance compensation voltage V_(ic), which isconfigured to cancel all or a portion of a source impedance voltage,which, as discussed above is generated due to the supply current iprovided across the source impedance presented by the one or more RFpower amplifiers 12. Accordingly, the impedance compensation voltageV_(ic) may be equal to but opposite the source impedance voltage, or asclose thereto as possible. As discussed above, the supply current I_(cc)is related to the RF input signal RF_(in). The power envelopemeasurement PE_(m) or the target voltage V_(t) can thus be used togenerate the impedance compensation voltage V_(ic) by performing anydesired transformation thereon, and using a known value for orestimation of the source impedance Z_(source), which may bepre-programmed or generated during a factory calibration process. Sincethe impedance compensation circuitry 78 uses the power envelopemeasurement PE_(m) or the target voltage V_(t), both of which have aknown relationship to the RF input signal RF_(in), an accurate estimateof the source impedance voltage can be provided, and thus the resultingimpedance compensation voltage V_(ic) can accurately cancel all or aportion thereof. The equalizer circuitry 80 provides equalization to theadjusted target supply voltage V_(ta) to provide an equalized adjustedtarget supply voltage V_(tea). In one embodiment, the equalizercircuitry 80 is configured to equalize the frequency response of the oneor more RF power amplifiers 12. The series inductor L and the shuntcapacitance C will result in a change in the response of the equivalentcircuit with respect to frequency. The equalizer circuitry 80 maycounter this effect in order to equalize the response over the frequencyof the one or more RF power amplifiers 12. Notably, the equalizercircuitry 80 utilizes the adjusted target voltage V_(ta) while theimpedance compensation circuitry 78 utilizes the power envelopemeasurement PE_(m) or the target voltage V_(t). That is, the equalizercircuitry 80 uses a time-adjusted or windowed version of the targetvoltage V_(t), while the impedance compensation circuitry 78 uses thepower envelope measurement PE_(m) or the target voltage V_(t), whichhave not been adjusted in time. The adder circuitry 82 adds theequalized adjusted target supply voltage V_(tea) and the impedancecompensation voltage V_(ic) to provide a compensated target supplyvoltage V_(tc). The envelope modulator circuitry 16 operates asdescribed above to generate the compensated envelope tracking supplyvoltage V_(cc(comp)) based on the compensated target supply voltageV_(tc).

As discussed above, there is some inherent delay between the powerenvelope measurement PE_(m) and the actual power envelope of the RFinput signal RF_(in), as well as between the target voltage V_(t) andthe actual power envelope of the RF input signal RF_(in). These delaysare caused in part by the functionality of the power envelope detectorcircuitry 24 and the LUT 26, respectively. In some cases, this mayinterfere with the ability of the impedance compensation circuitry 78 togenerate the impedance compensation voltage V_(ic) for cancellation ofthe source impedance voltage. Accordingly, additional envelopesynchronization circuitry 84 may be provided, as shown in FIG. 29. Theadditional envelope synchronization circuitry 84 is configured totime-align the power envelope measurement PE_(m) or the target voltageV_(t), depending on which is used, with the actual power envelope of theRF input signal RF_(in) to provide a time-aligned power envelopemeasurement PE_(mta), or a time-aligned target supply voltage V_(tta).The additional envelope synchronization circuitry 84 may use the delaymeasurement DEL_(m) from the delay measurement circuitry 32 to do so,effectively attempting to time delay or advance the power envelopemeasurement PE_(m) or the target supply voltage V_(t) as necessary togenerate the impedance compensation voltage V_(ic) so that it accuratelycancels the source impedance voltage. Notably, the time-alignmentperformed by the additional envelope synchronization circuitry 84 may bedifferent than that performed by the envelope synchronization circuitry30. With a time-aligned power envelope measurement PE_(mta) and/ortime-aligned target supply voltage V_(tta), the impedance compensationcircuitry 78 can accurately generate the impedance compensation voltageV_(ic) to partially or completely cancel the source impedance voltage.

To effectively equalize the frequency response of the one or more RFpower amplifiers 12 and cancel the effect of the source impedancevoltage, a combined transfer function of the impedance compensationcircuitry 78 and the equalizer circuitry 80 should be equal to Equation(23):

TF=1+L/R*s+LC*s ²  (23)

expressed in the Laplace domain. The first term L/R*s is primarilyresponsible for cancelling the source impedance voltage, while thesecond term LC*s² is primarily responsible for equalizing the frequencyresponse of the one or more RF power amplifiers 12. Accordingly, theimpedance compensation circuitry 78 may provide the portion of thetransfer function L/R*s with the power envelope measurement PE_(m), thetarget voltage V_(t), or another signal related to the RF input signalRF_(in) as an input discussed above. The equalizer circuitry 80 mayprovide the portion of the transfer function LC*s² with the adjustedtarget voltage V_(ta) as discussed above. The combination of the outputsfrom the impedance compensation circuitry 78 and the equalizer circuitry80 will equalize the frequency response of the one or more RF poweramplifiers 12 while cancelling the source impedance voltage.

FIG. 30 is a flow diagram illustrating a method for providing anenvelope tracking supply voltage according to an additional embodimentof the present disclosure. First, a power envelope measurement isreceived (step 300). As discussed above, the power envelope measurementmay be received via a coupler and measured by power envelope detectorcircuitry. A target supply voltage is then determined based on the powerenvelope measurement (step 302). As discussed above, the target supplyvoltage may be determined based on a look up in a LUT, which may beprovided according to an isogain contour for an RF power amplifier.Further, as discussed above, the target supply voltage may be delayedwith respect to an ideal supply voltage. Accordingly, the target supplyvoltage is adjusted based on a delay measurement (step 304), where thedelay measurement indicates an amount of delay between the powerenvelope of the RF signal and the envelope tracking supply voltage. Asdiscussed above, the target supply voltage may be adjusted by envelopesynchronization circuitry. The adjusted target supply voltage is thenequalized (step 306), resulting in an equalized adjusted target supplyvoltage. Any suitable equalization function may be applied to theadjusted target supply voltage, such as one that equalizes a bandwidthof the adjusted target supply voltage. The equalization may be performedby equalizer circuitry. An impedance compensation voltage is generatedbased on the power envelope of the RF signal (step 308), or any othersignal related thereto such as the target voltage V_(t). As discussedabove, the impedance compensation voltage is configured to cancel atleast a portion of a source impedance voltage, which is generated by asupply current being provided across a source impedance of one or moreRF amplifiers. The impedance compensation voltage may be generated byimpedance compensation circuitry. The equalized adjusted target supplyvoltage is then added to the impedance compensation voltage (step 310)to provide a compensated target supply voltage. This may be performed byadder circuitry. The envelope tracking supply voltage is then generatedbased on the compensated target supply voltage (step 312), e.g., viaenvelope tracking modulator circuitry. Details regarding each of thesteps, and in particular how the target supply voltage is adjusted toprovide the adjusted target supply voltage, are discussed above (see,e.g., Equations 1-13).

FIG. 31 illustrates details of the envelope synchronization circuitry 30according to one embodiment of the present disclosure. The envelopesynchronization circuitry 30 includes a first input 86A, a second input86B, an output 88, operational amplifier 90, control circuitry 92, afirst resistor R₁, a second resistor R₂, a capacitor C, a first switchSW₁, and a second switch SW₂. The first input 86A is configured toreceive a positive version of the target voltage V_(t), and is coupledto an inverting input of the operational amplifier 90 via the firstresistor R₁. The second input 86B is configured to receive a negativeversion of the target voltage −V_(t), and is coupled to the invertinginput of the operational amplifier 90 via the second switch SW₂ and thecapacitor C. The first switch SW₁ is coupled between the first input 86Aand the second input 86B. A non-inverting input of the operationalamplifier 90 is coupled to a reference voltage V_(ref), which could beany fixed voltage such as ground. An output of the operational amplifier90 is coupled to the output 88. The second resistor R₂ is coupledbetween the inverting input of the operational amplifier 90 and theoutput 88. The first resistor R₁ and the second resistor R₂ areadjustable resistors, such that a resistance thereof can be changed inresponse to a control signal provided thereto. The control circuitry 92is coupled to each of the first switch SW₁, the second switch SW₂, thefirst resistor R₂, and the second resistor R₂. In some embodiments thecapacitor C is an adjustable capacitor that is also coupled to thecontrol circuitry 92.

As discussed above, the envelope synchronization circuitry 30 isconfigured to receive and adjust the target voltage V_(t) to provide theadjusted target voltage V_(ta). In particular, the envelopesynchronization circuitry 30 is configured to adjust the target voltageV_(ta) so that it is synchronized in time with a power envelope of an RFsignal. To do so, the envelope synchronization circuitry 30 performsboth a linear and non-linear transform on the target voltage V_(t) asdiscussed above with respect to Equations (1-13). The exemplary envelopesynchronization circuitry 30 does so by implementing the transferfunction shown in Equations (24) and (25):

$\begin{matrix}\begin{matrix}{{TF_{1}} = {{- \frac{R_{2}}{R_{1}}}*\lbrack {1 + {R_{1}*C*s}} \rbrack}} & \;\end{matrix} & (24) \\{{TF_{2}} = {{- \frac{R_{2}}{R_{1}}}*\lbrack {1 - {R_{1}*C*s}} \rbrack}} & (25)\end{matrix}$

where the first transfer function TF₁ is provided when the first switchSW₁ is closed and the second switch SW₂ is open and the second transferfunction TF₂ is provided with the first switch SW₁ is open and thesecond switch SW₂ is closed. When the switches are arranged to providethe first transfer function TF₁, the envelope synchronization circuitry30 provides a positive group delay. When the switches are arranged toprovide the second transfer function TF₂, the envelope synchronizationcircuitry 30 provides a negative group delay. The amount of the groupdelay is dependent on the relationship between the resistance of thefirst resistor R₁, the resistance of the second resistor R₂, and thecapacitance of the capacitor C. The control circuitry 92 is configuredto operate the first switch SW₁ and the second switch SW₂ to provideeither a positive group delay having a desired magnitude, effectivelytime advancing the target voltage V_(t), or provide a negative groupdelay, effectively time delaying the target voltage V_(t). In additionto a positive or negative group delay, the envelope synchronizationcircuitry also provides a gain as indicated by the above transferfunctions. The control circuitry 92 is configured to change the gain ofthe envelope synchronization circuitry 30 by adjusting the value of thefirst resistor R₁, the second resistor R₂, and in some cases thecapacitance of the capacitor C in order to implement a non-linear gainfunction as discussed above to reduce overshooting during peaks of thetarget voltage V_(t). In particular, the control circuitry 92 may adjustthe value of the first resistor R₁, the second resistor R₂, and/or thecapacitor C to provide a non-linear gain response that is dependent onthe derivative of the target voltage dv_(t)/dt as discussed above withrespect to FIGS. 17A and 17B. Those skilled in the art will appreciatethat the first resistor R₁ and the second resistor R₂ may be implementedin any desirable fashion, such as by providing a static resistor inseries with a field-effect transistor or in parallel with a field-effecttransistor. The first switch SW₁ and the second switch SW₂ can similarlybe implemented in any desired manner.

Notably, the configuration for the envelope synchronization circuitry 30may be useful in other applications outside of the envelope trackingpower supply circuitry 22. In general, the topology shown may be used totime delay or advance any signal while providing a desired non-lineargain, and is not limited to use on the target voltage V_(t).

In some embodiments, instead of dynamically operating the first switchSW₁ and the second switch SW₂ to provide a positive group delay or anegative group delay while adjusting the first resistor R₁, the secondresistor R₂, and/or the capacitor C to provide a desired adjusted targetvoltage V_(ta) as discussed above, several versions of the circuitryshown in FIG. 31 may be provided and operated in a static fashion toseparately provide a time-advanced version of the adjusted targetvoltage V_(ta), a time-delayed version of the adjusted target voltageV_(ta), and a non-adjusted version of the adjusted target voltageV_(ta). A maximum signal detector may provide a maximum of these signalsas the adjusted target voltage V_(ta). In general, as discussed herein,the envelope synchronization circuitry 30 provides the adjusted targetvoltage V_(ta), which is either time-delayed or time-advanced such thatit is synchronized with a power envelope of an RF signal.

It is contemplated that any of the foregoing aspects, and/or variousseparate aspects and features as described herein, may be combined foradditional advantage. Any of the various embodiments as disclosed hereinmay be combined with one or more other disclosed embodiments unlessindicated to the contrary herein.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. Envelope synchronization circuitry comprising: atarget voltage input at which a target voltage is provided; an invertedtarget voltage input at which an inverted version of the target voltageis provided; an operational amplifier comprising an inverting input, anon-inverting input coupled to a fixed potential, and an output at whichan adjusted target supply voltage is provided; a first adjustableresistor coupled between the target voltage input and the invertinginput of the operational amplifier; a second adjustable resistor coupledbetween the inverting input of the operational amplifier and the outputof the operational amplifier; a capacitor coupled between the invertinginput and an intermediate node; a first switch coupled between theintermediate node and the target voltage input; and a second switchcoupled between the inverted target voltage input and the intermediatenode.
 2. The envelope synchronization circuitry of claim 1 furthercomprising control circuitry coupled to the first adjustable resistor,the second adjustable resistor, the first switch, and the second switch.3. The envelope synchronization circuitry of claim 2 wherein the controlcircuitry is configured to: in a first mode of operation, close thefirst switch and open the second switch such that the envelopesynchronization circuitry provides a negative group delay between thetarget voltage input and the output of the operational amplifier; and ina second mode of operation, open the first switch and close the secondswitch such that the envelope synchronization circuitry provides apositive group delay between the target voltage input and the output ofthe operational amplifier.
 4. The envelope synchronization circuitry ofclaim 3 wherein the control circuitry is further configured to adjust aresistance of the first adjustable resistor and a resistance of thesecond adjustable resistor to control a magnitude of group delay betweenthe target voltage input and the output of the operational amplifier. 5.The envelope synchronization circuitry of claim 4 wherein the controlcircuitry is configured to adjust the resistance of the first adjustableresistor and the resistance of the second adjustable resistor based on adelay measurement, wherein the delay measurement indicates a delaybetween the target voltage and a power envelope of an RF signal.
 6. Theenvelope synchronization circuitry of claim 5 wherein the controlcircuitry is further configured to adjust the resistance of the firstadjustable resistor and the resistance of the second adjustable resistorbased on a derivative of the target voltage over time.
 7. The envelopesynchronization circuitry of claim 6 wherein the control circuitry isfurther configured to adjust the resistance of the first adjustableresistor and the resistance of the second adjustable resistor such thata gain of the envelope synchronization circuitry is non-linear withrespect to the derivative of the target voltage over time.
 8. Theenvelope synchronization circuitry of claim 7 wherein the controlcircuitry is further configured to adjust the resistance of the firstadjustable resistor and the resistance of the second adjustable resistorsuch that the gain of the envelope synchronization circuitry isproportional to an absolute value of the derivative of the targetvoltage over time.
 9. A radio frequency (RF) system comprising: one ormore RF power amplifiers configured to amplify an RF input signal basedon an envelope tracking supply voltage to provide an RF output signal;envelope tracking power supply circuitry coupled to the one or more RFpower amplifiers and comprising: envelope synchronization circuitryconfigured to adjust a target supply voltage to provide an adjustedtarget supply voltage, the envelope synchronization circuitrycomprising: a target voltage input at which the target voltage isprovided; an inverted target voltage input at which an inverted versionof the target voltage is provided; an operational amplifier comprisingan inverting input, a non-inverting input coupled to a fixed potential,and an output at which the adjusted target supply voltage is provided; afirst adjustable resistor coupled between the target voltage input andthe inverting input of the operational amplifier; a second adjustableresistor coupled between the inverting input of the operationalamplifier and the output of the operational amplifier; a capacitorcoupled between the inverting input and an intermediate node; a firstswitch coupled between the intermediate node and the target voltageinput; and a second switch coupled between the inverted target voltageinput and the intermediate node; and envelope tracking modulatorcircuitry coupled to the envelope synchronization circuitry andconfigured to provide the envelope tracking supply voltage based on theadjusted target supply voltage.
 10. The RF system of claim 9 wherein theenvelope synchronization circuitry further comprises control circuitrycoupled to the first adjustable resistor, the second adjustableresistor, the first switch, and the second switch.
 11. The RF system ofclaim 10 wherein the control circuitry is configured to: in a first modeof operation, close the first switch and open the second switch suchthat the envelope synchronization circuitry provides a negative groupdelay between the target voltage input and the output of the operationalamplifier; and in a second mode of operation, open the first switch andclose the second switch such that the envelope synchronization circuitryprovides a positive group delay between the target voltage input and theoutput of the operational amplifier.
 12. The RF system of claim 11wherein the control circuitry is further configured to adjust aresistance of the first adjustable resistor and a resistance of thesecond adjustable resistor to control a magnitude of group delay betweenthe target voltage input and the output of the operational amplifier.13. The RF system of claim 12 wherein the control circuitry isconfigured to adjust the resistance of the first adjustable resistor andthe resistance of the second adjustable resistor based on a delaymeasurement, wherein the delay measurement indicates a delay between thetarget voltage and a power envelope of the RF input signal.
 14. The RFsystem of claim 13 wherein the control circuitry is further configuredto adjust the resistance of the first adjustable resistor and theresistance of the second adjustable resistor based on a derivative ofthe target voltage over time.
 15. The RF system of claim 14 wherein thecontrol circuitry is further configured to adjust the resistance of thefirst adjustable resistor and the resistance of the second adjustableresistor such that a gain of the envelope synchronization circuitry isnon-linear with respect to the derivative of the target voltage overtime.
 16. The RF system of claim 15 wherein the control circuitry isfurther configured to adjust the resistance of the first adjustableresistor and the resistance of the second adjustable resistor such thatthe gain of the envelope synchronization circuitry is proportional to anabsolute value of the derivative of the target voltage over time.